U.S. patent number 7,141,157 [Application Number 10/387,211] was granted by the patent office on 2006-11-28 for blending of low viscosity fischer-tropsch base oils and fischer-tropsch derived bottoms or bright stock.
This patent grant is currently assigned to Chevron U.S.A. Inc.. Invention is credited to David Kramer, Joseph Pudlak, John Rosenbaum.
United States Patent |
7,141,157 |
Rosenbaum , et al. |
November 28, 2006 |
Blending of low viscosity Fischer-Tropsch base oils and
Fischer-Tropsch derived bottoms or bright stock
Abstract
A process for preparing Fischer-Tropsch derived lubricating base
oils by blending a Fischer-Tropsch distillate fraction having a
viscosity of 2 or greater but less than 3 cSt at 100 degrees C.
with a Fischer-Tropsch derived bottoms fraction; lubricating base
oil compositions having a viscosity between about 3 and about 10
cSt at 100 degrees C. and a TGA Noack volatility of less than about
45 weight percent; and finished lubricants using the aforesaid
lubricating base oils.
Inventors: |
Rosenbaum; John (Richmond,
CA), Kramer; David (San Anselmo, CA), Pudlak; Joseph
(Vallejo, CA) |
Assignee: |
Chevron U.S.A. Inc. (San Ramon,
CA)
|
Family
ID: |
32961855 |
Appl.
No.: |
10/387,211 |
Filed: |
March 11, 2003 |
Prior Publication Data
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Document
Identifier |
Publication Date |
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US 20040178118 A1 |
Sep 16, 2004 |
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Current U.S.
Class: |
208/18; 585/502;
585/1; 508/110; 208/950; 208/19 |
Current CPC
Class: |
C10G
2/32 (20130101); C10M 111/02 (20130101); C10G
2300/1022 (20130101); C10N 2030/74 (20200501); C10M
2203/1085 (20130101); Y10S 208/95 (20130101); C10M
2203/1025 (20130101); C10G 2300/302 (20130101); C10G
2300/202 (20130101); C10G 2300/301 (20130101); C10G
2300/80 (20130101); C10G 2400/10 (20130101); C10N
2030/02 (20130101); C10N 2040/25 (20130101) |
Current International
Class: |
C10M
101/02 (20060101); C10M 105/02 (20060101) |
Field of
Search: |
;208/18,19,950 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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0 515 256 |
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Mar 1997 |
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EP |
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0 776 959 |
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Jun 1997 |
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EP |
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WO 99/41335 |
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Aug 1999 |
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WO |
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WO 00/08115 |
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Feb 2000 |
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WO |
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WO 00/14179 |
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Mar 2000 |
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WO |
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WO 00/14187 |
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Mar 2000 |
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WO |
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WO 02/070627 |
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Sep 2002 |
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WO |
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Other References
"Platforming of Paraffin Wax", Journal of the Institute of
Petroleum, 1956, vol. 43, pp. 205-216 by Schenk et al., University
of Chemical Engineering, Delft. cited by other .
"Hydro-Isomerization of Paraffin Wax", Journal of the Institute of
Petroleum, vol. 43, No. 407, pp. 297-306, Nov. 1957 by Breimer et
al., University of Chemical Engineering, Delft, Holland. cited by
other.
|
Primary Examiner: McAvoy; Ellen M.
Attorney, Agent or Firm: Roth; Steven H.
Claims
What is claimed is:
1. A process for producing a Fischer-Tropsch derived lubricating
base oil blend which comprises blending a Fischer-Tropsch
distillate fraction with a Fischer-Tropsch derived bottoms fraction
in the proper proportion to produce a Fischer-Tropsch derived
lubricating base oil characterized as having a kinematic viscosity
of between about 3 and about 10 cSt at 100 degrees C. and a TGA
Noack volatility of less than about 45 weight percent wherein said
distillate fraction is characterized by a kinematic viscosity of
about 2 cSt or greater but less than 3 cSt at 100 degrees C.
2. The process of claim 1 wherein the distillate fraction has a
viscosity between about 2.1 and 2.8 cSt at 100 degrees C.
3. The process of claim 2 wherein the distillate fraction has a
viscosity between about 2.2 and 2.7 cSt at 100 degrees C.
4. The process of claim 1 wherein the Fischer-Tropsch derived
bottoms fraction has a kinematic viscosity between about 9 cSt and
about 20 cSt at 100 degrees C.
5. The process of claim 4 wherein the bottoms fraction has a
viscosity of between about 10 and about 16 cSt at 100 degrees
C.
6. The process of claim 1 wherein the Fischer-Tropsch derived
bottoms fraction is bright stock.
7. The process of claim 6 wherein the bright stock is produced by
oligomerizing the olefins present in an olefin-containing
Fischer-Tropsch derived condensate.
8. The process of claim 7 including the preliminary step of
enriching the olefins in the Fischer-Tropsch condensate by the
dehydration of the alcohols present in the condensate.
9. The process of claim 7 including the preliminary step of
enriching the olefins in the Fischer-Tropsch condensate by the
thermal cracking of the hydrocarbons present in the condensate.
10. The process of claim 1 wherein the lubricating base oil blend
has a Noack volatility of less than 30 weight percent.
11. The process of claim 1 including the additional step of
blending the Fischer-Tropsch lubricating base oil blend with at
least one additive to produce a finished lubricant.
12. A process for producing a Fischer-Tropsch derived lubricating
base oil blends which comprises the steps of: a) separating a
Fisher-Tropsch derived condensate recovered from a Fischer-Tropsch
synthesis zone into at least a first olefin-containing distillate
fraction and a second Fischer-Tropsch distillate fraction, said
second light distillate fraction having a viscosity of about 2 cSt
or greater but less than 3 cSt at 100 degrees C.; b) oligomerizing
the olefins in the first olefin-containing distillate fraction to
produce a Fischer-Tropsch derived bright stock; c) blending the
second light Fischer-Tropsch distillate fraction with the
Fischer-Tropsch derived bright stock in the proper proportion to
produce a Fischer-Tropsch derived lubricating base oil
characterized as having a viscosity of between about 3 and about 10
cSt at 100 degrees C. and a TGA Noack volatility of less than about
45 weight percent.
13. The Fischer-Tropsch derived lubricating base oil blend of claim
12 wherein the first olefin-containing distillate fraction as
initially separated from the condensate also contains alcohols and
at least some of the olefins present in said first
olefin-containing distillate fraction are produced by the
dehydration of said alcohols.
14. The Fischer-Tropsch derived lubricating base oil blend of claim
12 wherein at least some of the olefins present in the first
olefin-containing distillate fraction are produced by cracking the
hydrocarbons present in said first olefin-containing distillate
fraction to produce an olefin enriched first distillate
fraction.
15. The process of claim 14 wherein at least some of the
hydrocarbons in the first olefin-containing distillate fraction are
cracked in a thermal cracking operation to produce the olefin
enriched first distillate fraction.
16. The process of claim 12 including the intermediate step of
isomerizing the bright stock prior blending it with the second
distillate fraction.
17. A Fischer-Tropsch derived lubricating base oil blend having a
viscosity of between about 3 and about 10 cSt at 100 degrees C. and
a TGA Noack volatility of less than about 45 weight percent said
Fischer-Tropsch derived lubricating base oil blend comprising a
Fischer-Tropsch distillate fraction and a Fischer-Tropsch derived
bottoms fraction wherein: (a) said distillate fraction is
characterized by a viscosity of about 2 cSt or greater but less
than 3 cSt at 100 degrees C. and (b) said Fischer-Tropsch derived
bottoms fraction is characterized by a viscosity of not less than
about 7 cSt at 100 degrees C.
18. The Fischer-Tropsch derived lubricating base oil blend of claim
17 wherein the distillate fraction has a viscosity between about
2.1 and 2.8 cSt at 100 degrees C.
19. The Fischer-Tropsch derived lubricating base oil blend of claim
18 wherein the distillate fraction has a viscosity between about
2.2 and 2.7 cSt at 100 degrees C.
20. The Fischer-Tropsch derived lubricating base oil of claim 17
having a boiling range distribution of at least 450 degrees F.
between the 5 percent and 95 percent points by analytical method
D-6352 or its equivalent.
21. The Fischer-Tropsch lubricating base oil of claim 17 wherein
the TGA Noack volatility is 12 weight percent or greater.
22. The Fischer-Tropsch lubricating base oil of claim 21 wherein
the TGA Noack volatility is greater than about 20 weight
percent.
23. The Fischer-Tropsch lubricating base oil blend of claim 17
wherein the TGA volatility is less than about 30 weight
percent.
24. The Fischer-Tropsch lubricating base oil of claim 17 wherein
the VI is between about 130 and about 185.
25. The Fischer-Tropsch lubricating base oil of claim 17 wherein
the total sulfur content is less than about 5 ppm.
26. The Fischer-Tropsch lubricating base oil of claim 17 wherein
the Fischer-Tropsch derived bottoms fraction comprises bright
stock.
27. The Fischer-Tropsch derived lubricating base oil of claim 26
wherein the cloud point of the blend is lower than the cloud point
of either the distillate fraction or the bright stock.
28. A Fischer-Tropsch derived lubricating base oil blend
characterized by a viscosity of between about 3 and about 10 cSt at
100 degrees C.; a TGA Noack volatility of less than 45 weight
percent; an initial boiling point within the range of between about
550 degrees F. and about 625 degrees F.; an end boiling point
between about 1000 degrees F. and about 1400 degrees F.; and
wherein less than 30 weight percent of the blend boils within the
region defined by the 50 percent boiling points, plus or minus 25
degrees F.
29. The Fischer-Tropsch derived lubricating base oil blend of claim
28 having a boiling range distribution of at least 450 degrees F.
between the 5 percent and 95 percent points as measured by
analytical method D-6352 or its equivalent.
30. The Fischer-Tropsch lubricating base oil blends of claim 28
wherein the TGA Noack volatility is 12 weight percent or
greater.
31. The Fischer-Tropsch lubricating base oil blend of claim 30
wherein the TGA volatility is greater than about 20 weight
percent.
32. The Fischer-Tropsch lubricating base oil blend of claim 28
wherein the TGA volatility is less than about 30 weight
percent.
33. The Fischer-Tropsch lubricating base oil blend of claim 28
wherein the VI is between about 130 and about 185.
34. The Fischer-Tropsch lubricating base oil blend of claim 28
wherein the total sulfur content is less than about 5 ppm.
35. A finished lubricant comprising a Fischer-Tropsch derived
lubricating base oil blend and at least one additive wherein the
Fischer-Tropsch derived lubricating base oil blend is characterized
by a viscosity of between about 3 and about 10 cSt at 100 degrees
C. and comprises a Fischer-Tropsch distillate fraction and a
Fischer-Tropsch derived bottoms fraction wherein: (a) said
distillate fraction is characterized by a viscosity of about 2 cSt
or greater but less than 3 cSt at 100 degrees C. and (b) said
Fischer-Tropsch derived bottoms fraction is characterized by a
viscosity of not less than about 9 cSt at 100 degrees C.
36. The finished lubricant of claim 35 wherein the lubricating base
oil blend has a Noack volatility of less than about 30 weight
percent.
37. The finished lubricant of claim 36 which is suitable for use as
an engine oil crankcase lubricant.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
This application is related to U.S. patent application Ser. No.
10/235,150 filed Sep. 4, 2002, titled "Blending of Low Viscosity
Fischer-Tropsch Base Oils to Produce High Quality Lubricating Base
Oils" and U.S. patent application Ser. No. 10/301,391 filed Nov.
20, 2002, titled "Blending of Low Viscosity Fischer-Tropsch Base
Oils With Conventional Base Oils to Produce High Quality
Lubricating Base Oils".
FIELD OF THE INVENTION
The invention relates to the blending of a low viscosity
Fischer-Tropsch derived base oil fraction with a higher viscosity
Fischer-Tropsch derived bottoms fraction to produce a high quality
lubricating base oil that is useful for preparing commercial
finished lubricants such as in crankcase engine oils.
BACKGROUND OF THE INVENTION
Finished lubricants and greases used for various applications,
including automobiles, diesel engines, natural gas engines, axles,
transmissions, and industrial applications consist of two general
components, a lubricating base oil and additives. Lubricating base
oil is the major constituent in these finished lubricants and
contributes significantly to the properties of the finished
lubricant. In general, a few lubricating base oils are used to
manufacture a wide variety of finished lubricants by varying the
mixtures of individual lubricating base oils and individual
additives.
Numerous governing organizations, including original equipment
manufacturers (OEM's), the American Petroleum Institute (API),
Association des Consructeurs d' Automobiles (ACEA), the American
Society of Testing and Materials (ASTM), the Society of Automotive
Engineers (SAE), and National Lubricating Grease Institute (NLGI)
among others, define the specifications for lubricating base oils
and finished lubricants. Increasingly, the specifications for
finished lubricants are calling for products with excellent low
temperature properties, high oxidation stability, and low
volatility. Currently only a small fraction of the base oils
manufactured today are able to meet the demanding specifications of
premium lubricant products.
Syncrudes prepared from the Fischer-Tropsch process comprise a
mixture of various solid, liquid, and gaseous hydrocarbons. Those
Fischer-Tropsch products which boil within the range of lubricating
base oil contain a high proportion of wax which makes them ideal
candidates for processing into lubricating base oil stocks.
Accordingly, the hydrocarbon products recovered from the
Fischer-Tropsch process have been proposed as feedstocks for
preparing high quality lubricating base oils. When the
Fischer-Tropsch waxes are converted into Fischer-Tropsch base oils
by various processes, such as hydroprocessing and distillation, the
base oils produced usually fall into different narrow-cut viscosity
ranges. Typically, the kinematic viscosity of the various cuts will
range between 2.1 cSt and 12 cSt at 100 degrees C. Since the
kinematic viscosity of lubricating base oils typically will fall
within the range of from 3 to 32 cSt at 100 degrees C., the base
oils that fall outside of this viscosity range have limited use
and, consequently, have less market value for engine oils.
The Fischer-Tropsch process typically produces a syncrude mixture
containing a wide range of products having varying molecular
weights but with a relatively high proportion of the products
characterized by a low molecular weight and viscosity. Used by
itself, this low viscosity product is not suitable for many
lubricant applications, especially high volume applications, such
as for engine oil. Currently, those Fischer-Tropsch derived base
oils having kinematic viscosities below 3 cSt at 100 degrees C.
have a limited market and are usually cracked into lower molecular
weight material, such as diesel and naphtha. However, diesel and
naphtha have a lower market value than lubricating base oil. It
would be desirable to be able to upgrade these low viscosity base
oils into products suitable for use as a lubricating base oil.
Conventional base oils prepared from petroleum derived feedstocks
having a kinematic viscosity below 3 cSt at 100 degrees C. have a
low viscosity index (VI) and high volatility. Consequently, low
viscosity conventional base oils are unsuitable for blending with
higher viscosity conventional base oils because the blend will fail
to meet the VI and volatility specifications for many finished
lubricants. Surprisingly, it has been found that Fischer-Tropsch
derived base oils having a kinematic viscosity above 2 and below 3
cSt at 100 degrees C. display unusually high VI's, resulting in
excellent low temperature properties and volatilities similar to
those seen in conventional Group I and Group II light neutral base
oils which have a kinematic viscosity generally falling in the
range of between 3.8 and 4.7 cSt at 100 degrees C. Even more
surprising was that when the low viscosity Fischer-Tropsch derived
base oils were blended with certain Fischer-Tropsch derived bottom
fractions or bright stock, a VI premium was observed, i.e., the VI
of the blend was significantly higher than would have been expected
from a mere averaging of the VI's for the two fractions.
Consequently, it is has been discovered that the low viscosity
Fischer-Tropsch base oils fractions may be advantageously employed
as blending stock to prepare premium lubricants.
While Fischer-Tropsch derived lubricating base oil blends have been
described in the prior art, the method used to prepare them and the
properties of the prior art blends differ from the present
invention. See, for example, U.S. Pat. Nos. 6,332,974; 6,096,940;
4,812,246; and 4,906,350. It has not been previously taught that
Fischer-Tropsch fractions having a viscosity of less than 3 cSt at
100 degrees C. could be used to prepare lubricating base oils
suitable for blending finished lubricants meeting the
specifications for SAE Grade 10W, and 15W multigrade engine oils;
monograde engine oils, automatic transmission fluids; and ISO
Viscosity Grade 22, 32, and 46 industrial oils. With the present
invention, this becomes possible.
When referring to conventional lubricating base oils this
disclosure is referring to conventional petroleum derived
lubricating base oils produced using petroleum refining processes
well documented in the literature and known to those skilled in the
art.
As used in this disclosure the word "comprises" or "comprising" is
intended as an open-ended transition meaning the inclusion of the
named elements, but not necessarily excluding other unnamed
elements. The phrase "consists essentially of" or "consisting
essentially of" is intended to mean the exclusion of other elements
of any essential significance to the composition. The phrase
"consisting of" or "consists of" are intended as a transition
meaning the exclusion of all but the recited elements with the
exception of only minor traces of impurities.
SUMMARY OF THE INVENTION
The present invention is directed to a process for producing a
Fischer-Tropsch derived lubricating base oil blend which comprises
blending a Fischer-Tropsch distillate fraction with a
Fischer-Tropsch derived bottoms fraction in the proper proportion
to produce a Fischer-Tropsch derived lubricating base oil
characterized as having a kinematic viscosity of between about 3
and about 10 cSt at 100 degrees C. and a TGA Noack volatility of
less than about 45 weight percent wherein said distillate fraction
is characterized by a kinematic viscosity of about 2 cSt or greater
but less than 3 cSt at 100 degrees C.
The Fischer-Tropsch derived bottoms fraction will generally have a
kinematic viscosity at 100 degrees C. of not less than about 7 cSt.
The Fischer-Tropsch derived bottoms fraction may constitute that
residual fraction remaining at the bottom of the vacuum column
following the fractionation of the waxy material recovered directly
from Fischer-Tropsch syncrude, or it may be prepared from the
condensate fraction by the oligomerization of the olefins present.
Except for bright stock, most Fischer-Tropsch bottoms fractions
will have a kinematic viscosity within the range of from about 9
cSt to about 20 cSt at 100 degrees C., preferably, between about 10
cSt and 16 cSt. However, in the case of Fischer-Tropsch derived
bright stock the kinematic viscosity may be considerably higher.
The invention makes it possible to upgrade the low viscosity
Fischer-Tropsch derived base oils into more valuable premium
lubricants which otherwise would be cracked or blended into lower
value transportation fuels.
Bright stock constitutes a bottoms fraction which has been highly
refined and dewaxed. Bright stock is a high viscosity base oil.
Conventional petroleum derived bright stock is named for the SUS
viscosity at 210 degrees F., having viscosities above 180 cSt at 40
degrees C., preferably above 250 cSt at 40 degrees C., and more
preferably ranging from 500 to 1100 cSt at 40 degrees C.
Fischer-Tropsch derived bright stock has a kinematic viscosity
between about 15 cSt and about 40 cSt at 100 degrees C. Bright
stock used to carry out the invention may be produced from
Fischer-Tropsch derived residual stocks recovered from the bottom
of the vacuum column following the fractionation of the waxy
product separated from the syncrude from the Fischer-Tropsch plant.
However, Fischer-Tropsch derived bright stock may also be prepared
from the oligomerization of the olefins present in the
Fischer-Tropsch condensate recovered from the Fischer-Tropsch
reactor. Blending Fischer-Tropsch derived bright stock with the
Fischer-Tropsch derived distillate fraction produces a lubricating
base oil having especially low volatility, good cold flow
properties, and improved oxidation stability as compared to many
conventional base oils.
Lubricating base oils falling within the scope of the invention are
blends of at least two different fractions. One fraction is a light
distillate fraction and the other fraction is a bottoms fraction.
Accordingly, lubricating base oils of the invention are
distinguished from those homogeneous lubricating base oils prepared
from a single distillate fraction or from only a bottoms fraction.
Consequently, the Fischer-Tropsch lubricating base oil blends
prepared using the process of the present invention are unique, and
will display certain properties which may be used to distinguish
the blends from both conventional and from other Fischer-Tropsch
derived lubricating base oils disclosed in the prior art. For
example, lubricating base oil blends prepared according to the
invention will have a TGA Noack volatility of greater than about 12
and more generally will have a TGA Noack volatility in excess of
about 20. However, if the blends are intended for use as crankcase
lubricating oils they will preferably have a Noack volatility of
less than about 30 weight percent. The blends also typically will
display a VI of between about 130 and about 185 and will have very
low total sulfur, usually less than about 5 ppm. Most noticeably,
the lubricating base oils compositions of the invention display
unique boiling range distributions.
The boiling range distributions characteristic of the lubricating
base oils prepared according to the invention will depend to some
extent on the properties of the Fischer-Tropsch derived bottoms
fraction used in preparing the blend. In general, the lubricating
base oils of the invention will have an initial boiling point
within the range of between about 550 degrees F. (288 degrees C.)
and about 625 degrees F. (330 degrees C.) and an end boiling point
between about 1000 degrees F. (538 degrees C.) and about 1400
degrees F. (760 degrees C.). In addition, lubricating base oils of
the invention will typically display a bi-modal boiling range
distribution which may be described as a lubricating base oil blend
in which less than 20 weight percent of the blend will boil within
the region defined by the 50 percent boiling points, plus or minus
30 degrees F.
All boiling range distributions in this disclosure are measured
using the standard analytical method D-6352 or its equivalent
unless stated otherwise. As used herein, a equivalent analytical
method to D-6352 refers to any analytical method which gives
substantially the same results as the standard method.
The Fischer-Tropsch derived lubricating base oil blends prepared
according to the present invention also may be blended with
conventionally derived lubricating base oils, such as conventional
neutral Group I and Group II lubricating base oils. When the
Fischer-Tropsch derived lubricating base oil is blended with a
conventional neutral Group I or Group II base oil, the conventional
base oil will typically comprise between about 40 weight percent
and about 90 weight percent of the total blend, with from about 40
weight percent to about 70 weight percent being preferred.
The Fischer-Tropsch derived lubricating base oil blends of the
invention may also be blended with synthetic lubricants, such as
esters (mono-, di-, dimer-, polyol-, and aromatic),
polyalphaolefins. Polyphenyl ethers and polygycols.
Lubricating base oil blends of the invention represent premium
lubricants which may be used to prepare finished lubricants. A
finished lubricant, such as, for example, a commercial multi-grade
crankcase lubricating oil meeting SAE J300, June 2001
specifications, may be prepared from the lubricating base oil
blends of the invention by the addition of the proper additives.
Typical additives added to a lubricating base oil blend when
preparing a finished lubricant include anti-wear additives,
detergents, dispersants, antioxidants, pour point depressants, VI
improvers, friction modifiers, demulsifiers, antifoaming agents,
corrosion inhibitors, seal swell agents, and the like. In addition,
commercial products meeting SAE standards for gear lubricants, NLGI
Mark GC and LB for greases, and ISO Viscosity Grade standards for
industrial oils may be prepared from the Fischer-Tropsch derived
lubricating base oils of the invention.
DETAILED DESCRIPTION OF THE INVENTION
Noack volatility of engine oil, as measured by TGA Noack and
similar methods, has been found to correlate with oil consumption
in passenger car engines. Strict requirements for low volatility
are important aspects of several recent engine oil specifications,
such as, for example, ACEA A-3 and B-3 in Europe and ILSAC GF-3 in
North America. Due to the high volatility of conventional low
viscosity oils with kinematic viscosities below 3 cSt at 100
degrees C., they have limited their use in passenger car engine
oils. Any new lubricating base oil stocks developed for use in
automotive engine oils should have a volatility no greater than
current conventional Group I or Group II light neutral oils.
Fischer-Tropsch wax processing typically produces a relatively high
proportion of products of low molecular weight and low viscosity
that are processed into light products such as naphtha, gasoline,
diesel, fuel oil, or kerosene. A proportion of products have
kinematic viscosities above 3.0 cSt which are useful directly as
lubricating base oils for many different products, including engine
oils. Those base oils with kinematic viscosities between 2.1 and
2.8 cSt typically are further processed into lighter products
(e.g., gasoline or diesel) in order to be of much economic value.
Alternatively, these low viscosity Fischer-Tropsch derived base
oils may be used in light industrial oils, such as, for example,
utility oils, transformer oils, pump oils, or hydraulic oils; many
of which have less stringent volatility requirements, and all of
which are in much lower demand than engine oils.
Lubricating base oils for use in engine oils are in higher demand
than those for use in light products. The ability to use a higher
proportion of the products from Fischer-Tropsch processes in
lubricating base oil blends for engine oils is highly desirable. By
virtue of the present invention, Fischer-Tropsch derived
lubricating base oils characterized by low viscosity are blended
with a Fischer-Tropsch derived bottoms fraction to produce
compositions which are useful as a lubricating base oil for
preparing engine oil. The lubricating base oil stocks of this
invention are comparable in volatility and viscosity to
conventional Group I and Group II neutral oils. In addition,
lubricating base oils of the invention also have other improved
properties, such as very low sulfur and exceptional oxidation
stability.
Fischer-Tropsch Synthesis
During Fischer-Tropsch synthesis liquid and gaseous hydrocarbons
are formed by contacting a synthesis gas (syngas) comprising a
mixture of hydrogen and carbon monoxide with a Fischer-Tropsch
catalyst under suitable temperature and pressure reactive
conditions. The Fischer-Tropsch reaction is typically conducted at
temperatures of from about 300 degrees to about 700 degrees F.
(about 150 degrees to about 370 degrees C.) preferably from about
400 degrees to about 550 degrees F. (about 205 degrees to about 290
degrees C.); pressures of from about 10 to about 600 psia, (0.7 to
41 bars) preferably 30 to 300 psia, (2 to 21 bars) and catalyst
space velocities of from about 100 to about 10,000 cc/g/hr.,
preferably 300 to 3,000 cc/g/hr.
The products from the Fischer-Tropsch synthesis may range from
C.sub.1 to C.sub.200 plus hydrocarbons with a majority in the
C.sub.5 C.sub.100 plus range. The reaction can be conducted in a
variety of reactor types, such as, for example, fixed bed reactors
containing one or more catalyst beds, slurry reactors, fluidized
bed reactors, or a combination of different types of reactors. Such
reaction processes and reactors are well known and documented in
the literature. The slurry Fischer-Tropsch process, which is
preferred in the practice of the invention, utilizes superior heat
(and mass) transfer characteristics for the strongly exothermic
synthesis reaction and is able to produce relatively high molecular
weight paraffinic hydrocarbons when using a cobalt catalyst. In the
slurry process, a syngas comprising a mixture of hydrogen and
carbon monoxide is bubbled up as a third phase through a slurry
which comprises a particulate Fischer-Tropsch type hydrocarbon
synthesis catalyst dispersed and suspended in a slurry liquid
comprising hydrocarbon products of the synthesis reaction which are
liquid under the reaction conditions. The mole ratio of the
hydrogen to the carbon monoxide may broadly range from about 0.5 to
about 4, but is more typically within the range of from about 0.7
to about 2.75 and preferably from about 0.7 to about 2.5. A
particularly preferred Fischer-Tropsch process is taught in
European Patent Application No. 0609079, also completely
incorporated herein by reference for all purposes.
Suitable Fischer-Tropsch catalysts comprise one or more Group VIII
catalytic metals such as Fe, Ni, Co, Ru and Re, with cobalt being
preferred. Additionally, a suitable catalyst may contain a
promoter. Thus, a preferred Fischer-Tropsch catalyst comprises
effective amounts of cobalt and one or more of Re, Ru, Pt, Fe, Ni,
Th, Zr, Hf, U, Mg and La on a suitable inorganic support material,
preferably one which comprises one or more refractory metal oxides.
In general, the amount of cobalt present in the catalyst is between
about 1 and about 50 weight percent of the total catalyst
composition. The catalysts can also contain basic oxide promoters
such as ThO.sub.2, La.sub.2O.sub.3, MgO, and TiO.sub.2, promoters
such as ZrO.sub.2, noble metals (Pt, Pd, Ru, Rh, Os, Ir), coinage
metals (Cu, Ag, Au), and other transition metals such as Fe, Mn,
Ni, and Re. Suitable support materials include alumina, silica,
magnesia and titania or mixtures thereof. Preferred supports for
cobalt containing catalysts comprise titania. Useful catalysts and
their preparation are known and illustrated in U.S. Pat. No.
4,568,663, which is intended to be illustrative but non-limiting
relative to catalyst selection.
The products as they are recovered from the Fischer-Tropsch
operation usually may be divided into three fractions, a gaseous
fraction consisting of very light products, a condensate fraction
generally boiling in the range of naphtha and diesel, and a high
boiling Fischer-Tropsch wax fraction which is normally solid at
ambient temperatures. The Fischer-Tropsch derived products used to
prepare base oils are usually prepared from the waxy fractions of
the Fischer-Tropsch syncrude by hydrotreating and/or
hydroisomerization. Other methods which may be used in preparing
the base oils include oligomerization, solvent dewaxing,
atmospheric and vacuum distillation, hydrocracking, hydrofinishing,
and other forms of hydroprocessing.
Hydroisomerization and Solvent Dewaxing
Hydroisomerization, or for the purposes of this disclosure simply
"isomerization", is intended to improve the cold flow properties of
the Fischer-Tropsch derived product by the selective addition of
branching into the molecular structure. Isomerization ideally will
achieve high conversion levels of the Fischer-Tropsch wax to
non-waxy iso-paraffins while at the same time minimizing the
conversion by cracking. Since wax conversion can be complete, or at
least very high, this process typically does not need to be
combined with additional dewaxing processes to produce a
lubricating oil base stock with an acceptable pour point.
Isomerization operations suitable for use with the present
invention typically uses a catalyst comprising an acidic component
and may optionally contain an active metal component having
hydrogenation activity. The acidic component of the catalysts
preferably includes an intermediate pore SAPO, such as SAPO-11,
SAPO-31, and SAPO-41, with SAPO-11 being particularly preferred.
Intermediate pore zeolites, such as ZSM-22, ZSM-23, SSZ-32, ZSM-35,
and ZSM-48, also may be used in carrying out the isomerization.
Typical active metals include molybdenum, nickel, vanadium, cobalt,
tungsten, zinc, platinum, and palladium. The metals platinum and
palladium are especially preferred as the active metals, with
platinum most commonly used.
The phrase "intermediate pore size", when used herein, refers to an
effective pore aperture in the range of from about 4.0 to about 7.1
Angstrom when the porous inorganic oxide is in the calcined form.
Molecular sieves having pore apertures in this range tend to have
unique molecular sieving characteristics. Unlike small pore
zeolites such as erionite and chabazite, they will allow
hydrocarbons having some branching into the molecular sieve void
spaces. Unlike larger pore zeolites such as faujasites and
mordenites, they are able to differentiate between n-alkanes and
slightly branched alkenes, and larger alkanes having, for example,
quaternary carbon atoms. See U.S. Pat. No. 5,413,695. The term
"SAPO" refers to a silicoaluminophosphate molecular sieve such as
described in U.S. Pat. Nos. 4,440,871 and 5,208,005.
In preparing those catalysts containing a non-zeolitic molecular
sieve and having an hydrogenation component, it is usually
preferred that the metal be deposited on the catalyst using a
non-aqueous method. Non-zeolitic molecular sieves include
tetrahedrally-coordinated [AlO2 and PO2] oxide units which may
optionally include silica. See U.S. Pat. No. 5,514,362. Catalysts
containing non-zeolitic molecular sieves, particularly catalysts
containing SAPO's, on which the metal has been deposited using a
non-aqueous method have shown greater selectivity and activity than
those catalysts which have used an aqueous method to deposit the
active metal. The non-aqueous deposition of active metals on
non-zeolitic molecular sieves is taught in U.S. Pat. No. 5,939,349.
In general, the process involves dissolving a compound of the
active metal in a non-aqueous, non-reactive solvent and depositing
it on the molecular sieve by ion exchange or impregnation.
Solvent dewaxing attempts to remove the waxy molecules from the
product by dissolving them in a solvent, such as methyl ethyl
ketone, methyl iso-butyl ketone, or toluene, and precipitating the
wax molecules and then removing them by filtration as discussed in
Chemical Technology of Petroleum, 3.sup.rd Edition, William Gruse
and Donald Stevens, McGraw-Hill Book Company, Inc., New York, 1960,
pages 566 570. See also U.S. Pat. Nos. 4,477,333; 3,773,650; and
3,775,288. In general, with the present invention isomerization is
usually preferred over solvent dewaxing, since it results in higher
viscosity index products with improved low temperature properties,
and in higher yields of the products boiling within the range of
the light distillate fraction and the heavy fraction. However
solvent dewaxing may be advantageously used in combination with
isomerization to recover unconverted wax following
isomerization.
Hydrotreating, Hydrocracking, and Hydrofinishing
Hydrotreating refers to a catalytic process, usually carried out in
the presence of free hydrogen, in which the primary purpose is the
removal of various metal contaminants, such as arsenic;
heteroatoms, such as sulfur and nitrogen; or aromatics from the
feed stock. Generally, in hydrotreating operations cracking of the
hydrocarbon molecules, i.e., breaking the larger hydrocarbon
molecules into smaller hydrocarbon molecules, is minimized, and the
unsaturated hydrocarbons are either fully or partially
hydrogenated.
Hydrocracking refers to a catalytic process, usually carried out in
the presence of free hydrogen, in which the cracking of the larger
hydrocarbon molecules is the primary purpose of the operation.
Desulfurization and/or denitrification of the feedstock also
usually will occur. Although typically hydrocracking operations
will usually be limited to the cracking of the heaviest bottoms
material, in the present invention it is one method that may be
used to increase amount of olefins present in the Fischer-Tropsch
condensate recovered from the Fischer-Tropsch synthesis operation.
The olefin enriched distillate fraction produced from the
condensate may be oligomerized to prepare bright stock which is
blended with the light fraction to prepare lubricating base oils
within the scope of the invention.
Catalysts used in carrying out hydrotreating and hydrocracking
operations are well known in the art. See for example U.S. Pat.
Nos. 4,347,121 and 4,810,357, the contents of which are hereby
incorporated by reference in their entirety, for general
descriptions of hydrotreating, hydrocracking, and of typical
catalysts used in each of the processes. Suitable catalysts include
noble metals from Group VIIIA (according to the 1975 rules of the
International Union of Pure and Applied Chemistry), such as
platinum or palladium on an alumina or siliceous matrix, and Group
VIII and Group VIB, such as nickel-molybdenum or nickel-tin on an
alumina or siliceous matrix. U.S. Pat. No. 3,852,207 describes a
suitable noble metal catalyst and mild conditions. Other suitable
catalysts are described, for example, in U.S. Pat. Nos. 4,157,294
and 3,904,513. The non-noble hydrogenation metals, such as
nickel-molybdenum, are usually present in the final catalyst
composition as oxides, but are usually employed in their reduced or
sulfided forms when such sulfide compounds are readily formed from
the particular metal involved. Preferred non-noble metal catalyst
compositions contain in excess of about 5 weight percent,
preferably about 5 to about 40 weight percent molybdenum and/or
tungsten, and at least about 0.5, and generally about 1 to about 15
weight percent of nickel and/or cobalt determined as the
corresponding oxides. Catalysts containing noble metals, such as
platinum, contain in excess of 0.01 percent metal, preferably
between 0.1 and 1.0 percent metal. Combinations of noble metals may
also be used, such as mixtures of platinum and palladium.
The hydrogenation components can be incorporated into the overall
catalyst composition by any one of numerous procedures. The
hydrogenation components can be added to matrix component by
co-mulling, impregnation, or ion exchange and the Group VI
components, i.e.; molybdenum and tungsten can be combined with the
refractory oxide by impregnation, co-mulling or
co-precipitation.
The matrix component can be of many types including some that have
acidic catalytic activity. Ones that have activity include
amorphous silica-alumina or zeolitic or non-zeolitic crystalline
molecular sieves. Examples of suitable matrix molecular sieves
include zeolite Y, zeolite X and the so called ultra stable zeolite
Y and high structural silica-alumina ratio zeolite Y such as that
described in U.S. Pat. Nos. 4,401,556; 4,820,402; and 5,059,567.
Small crystal size zeolite Y, such as that described in U.S. Pat.
No. 5,073,530 can also be used. Non-zeolitic molecular sieves which
can be used include, for example, silicoaluminophosphates (SAPO),
ferroaluminophosphate, titanium aluminophosphate and the various
ELAPO molecular sieves described in U.S. Pat. No. 4,913,799 and the
references cited therein. Details regarding the preparation of
various non-zeolite molecular sieves can be found in U.S. Pat. No.
5,114,563 (SAPO) and U.S. Pat. No. 4,913,799 and the various
references cited in U.S. Pat. No. 4,913,799. Mesoporous molecular
sieves can also be used, for example the M41S family of materials
as described in J. Am. Chem. Soc., 114:10834 10843(1992)), MCM-41;
U.S. Pat. Nos. 5,246,689; 5,198,203; and 5,334,368; and MCM-48
(Kresge et al., Nature 359:710 (1992)). Suitable matrix materials
may also include synthetic or natural substances as well as
inorganic materials such as clay, silica and/or metal oxides such
as silica-alumina, silica-magnesia, silica-zirconia, silica-thoria,
silica-berylia, silica-titania as well as ternary compositions,
such as silica-alumina-thoria, silica-alumina-zirconia,
silica-alumina-magnesia, and silica-magnesia zirconia. The lafter
may be either naturally occurring or in the form of gelatinous
precipitates or gels including mixtures of silica and metal oxides.
Naturally occurring clays which can be composited with the catalyst
include those of the montmorillonite and kaolin families. These
clays can be used in the raw state as originally mined or initially
subjected to dealumination, acid treatment or chemical
modification.
In performing the hydrocracking and/or hydrotreating operation,
more than one catalyst type may be used in the reactor. The
different catalyst types can be separated into layers or mixed.
Hydrocracking conditions have been well documented in the
literature. In general, the overall LHSV is about 0.1 hr.sup.-1 to
about 15.0 hr.sup.-1 (v/v), preferably from about 0.25 hr.sup.-1 to
about 2.5 hr.sup.-1. The reaction pressure generally ranges from
about 500 psig to about 3500 psig (about 10.4 MPa to about 24.2
MPa, preferably from about 1500 psig to about 5000 psig (about 3.5
MPa to about 34.5 MPa). Hydrogen consumption is typically from
about 500 to about 2500 SCF per barrel of feed (89.1 to 445 m.sup.3
H2/m.sup.3 feed). Temperatures in the reactor will range from about
400 degrees F. to about 950 degrees F. (about 204 degrees C. to
about 510 degrees C.), preferably ranging from about 650 degrees F.
to about 850 degrees F. (about 343 degrees C. to about 454 degrees
C.).
Typical hydrotreating conditions vary over a wide range. In
general, the overall LHSV is about 0.25 to 2.0, preferably about
0.5 to 1.0. The hydrogen partial pressure is greater than 200 psia,
preferably ranging from about 500 psia to about 2000 psia. Hydrogen
recirculation rates are typically greater than 50 SCF/Bbl, and are
preferably between 1000 and 5000 SCF/Bbl. Temperatures in the
reactor will range from about 300 degrees F. to about 750 degrees
F. (about 150 degrees C. to about 400 degrees C.), preferably
ranging from 450 degrees F. to 600 degrees F. (230 degrees C. to
about 315 degrees C.).
Hydrotreating may also be used as a final step in the lube base oil
manufacturing process. This final step, commonly called
hydrofinishing, is intended to improve the UV stability and
appearance of the product by removing traces of aromatics, olefins,
color bodies, and solvents. As used in this disclosure, the term UV
stability refers to the stability of the lubricating base oil or
the finished lubricant when exposed to UV light and oxygen.
Instability is indicated when a visible precipitate forms, usually
seen as floc or cloudiness, or a darker color develops upon
exposure to ultraviolet light and air. A general description of
hydrofinishing may be found in U.S. Pat. Nos. 3,852,207 and
4,673,487. Clay treating to remove these impurities is an
alternative final process step.
Thermal Cracking
Thermal cracking may also be employed to crack the paraffin
molecules into lower molecular weight olefins in order to olefin
enrich the Fischer-Tropsch condensate. As already noted, all
Fischer-Tropsch syncrude as initially recovered from the
Fischer-Tropsch synthesis will contain olefins. By thermal cracking
the paraffin molecules present in the condensate fraction the
amount of olefins present may be significantly increased. Following
the thermal cracking operation the condensate fraction should have
an olefinicity of at least 20 percent by weight, preferably at
least 40 percent by weight, and most preferably at least 50 percent
by weight.
Although batch pyrolysis reactors, such as employed in delayed
coking or in cyclic batch operations, could be used to carry out
this operation, generally a continuous flow-through operation is
preferred in which the feed is first preheated to a temperature
sufficient to vaporize most or all of the feed after which the
vapor is passed through a tube or tubes. A desirable option is to
bleed any remaining nonvaporized hydrocarbons prior to entering the
tubes in the cracking furnace. Preferably, the thermal cracking is
conducted in the presence of steam which serves as a heat source
and also helps suppress coking in the reactor. Details of a typical
steam thermal cracking process may be found in U.S. Pat. No.
4,042,488, hereby incorporated by reference in its entirety.
Although catalyst is generally not used in carrying out the thermal
cracking operation, it is possible to conduct the operation in a
fluidized bed in which the vaporized feed is contacted with hot
fluidized inert particles, such as fluidized particles of coke.
In performing the thermal cracking operation, it is preferable that
the feed be maintained in the vapor phase during the cracking
operation to maximize the production of olefins. Liquid phase
cracking results in the formation of significant amounts of
paraffins which are unreactive in the oligomerization operation
and, therefore, are not desired. In the pyrolysis zone, the
cracking conditions should be sufficient to provide a cracking
conversion of greater than about 30 percent by weight of the
paraffins present. Preferably, the cracking conversion will be at
least 50 percent by weight and most preferably at least 70 percent
by weight. The optimal temperature and other conditions in the
pyrolysis zone for the cracking operation will vary somewhat
depending on the feed. In general, the temperature must be high
enough to maintain the feed in the vapor phase but not so high that
the feed is overcracked, i.e., the temperature and conditions
should not be so severe that excessive C.sub.4 minus hydrocarbons
are generated. The temperature in the pyrolysis zone normally will
be maintained at a temperature of between about 950 degrees F. (510
degrees C.) and about 1600 degrees F. (870 degrees C.). The optimal
temperature range for the pyrolysis zone in order to maximize the
production of olefins from the Fischer-Tropsch wax will depend upon
the endpoint of the feed. In general, the higher the carbon number,
the higher the temperature required to achieve maximum conversion.
Accordingly, some routine experimentation may be necessary to
identify the optimal cracking conditions for a specific feed. The
pyrolysis zone usually will employ pressures maintained between
about 0 atmospheres and about 5 atmospheres, with pressures in the
range of from about 0 to about 2 generally being preferred.
Although the optimal residence time of the wax fraction in the
reactor will vary depending on the temperature and pressure in the
pyrolysis zone, typical residence times are generally in the range
of from about 1.5 seconds to about 500 seconds, with the preferred
range being between about 5 seconds and about 300 seconds.
Oligomerization
Depending upon how the Fischer-Tropsch synthesis is carried out,
the Fischer-Tropsch condensate will contain varying amounts of
olefins. In addition, most Fischer-Tropsch condensate will contain
some alcohols which may be readily converted into olefins by
dehydration. As already noted, the condensate may also be olefin
enriched through a cracking operation, either by means of
hydrocracking or more preferably by thermal cracking. In one
embodiment of the present invention these olefins may be
oligomerized to produce a Fischer-Tropsch derived bright stock.
During oligomerization the lighter olefins are not only converted
into heavier molecules, but the carbon backbone of the oligomers
will also display branching at the points of molecular addition.
Due to the introduction of branching into the molecule, the pour
point of the products is reduced.
The oligomerization of olefins has been well reported in the
literature, and a number of commercial processes are available.
See, for example, U.S. Pat.
Nos. 4,417,088; 4,434,308; 4,827,064; 4,827,073; and 4,990,709.
Various types of reactor configurations may be employed, with the
fixed catalyst bed reactor being used commercially. More recently,
performing the oligomerization in an ionic liquid media has been
proposed, since these catalysts are very active, and the contact
between the catalyst and the reactants is efficient and the
separation of the catalyst from the oligomerization products is
facilitated. The oligomerization reaction will proceed over a wide
range of conditions. Typical temperatures for carrying out the
reaction are between about 32 degrees F. (0 degrees C.) and about
800 degrees F. (425 degrees C.). Other conditions include a space
velocity from 0.1 to 3 LHSV and a pressure from 0 to 2000 psig.
Catalysts for the oligomerization reaction can be virtually any
acidic material, such as, for example, zeolites, clays, resins,
BF.sub.3 complexes, HF, H.sub.2SO.sub.4, AlCl.sub.3, ionic liquids
(preferably ionic liquids containing a Bronsted or Lewis acidic
component or a combination of Bronsted and Lewis acid components),
transition metal-based catalysts (such as Cr/SiO.sub.2),
superacids, and the like. In addition, non-acidic oligomerization
catalysts including certain organometallic or transition metal
oligomerization catalysts may be used, such as, for example,
zirconocenes.
Distillation
The separation of the Fischer-Tropsch derived products into the
various fractions used in the process of the invention is generally
conducted by either atmospheric or vacuum distillation or by a
combination of atmospheric and vacuum distillation. Atmospheric
distillation is typically used to separate the lighter distillate
fractions, such as naphtha and middle distillates, from a bottoms
fraction having an initial boiling point above about 700 degrees F.
to about 750 degrees F. (about 370 degrees C. to about 400 degrees
C.). At higher temperatures thermal cracking of the hydrocarbons
may take place leading to fouling of the equipment and to lower
yields of the heavier cuts. Vacuum distillation is typically used
to separate the higher boiling material, such as the lubricating
base oil fractions.
As used in this disclosure, the term "distillate fraction" or
"distillate" refers to a side stream product recovered either from
an atmospheric fractionation column or from a vacuum column as
opposed to the "bottom fraction" which represents the residual
higher boiling fraction recovered from the bottom of the column. In
this disclosure, the term "bottoms" also includes those bottoms
fractions and bright stock derived from the oligomerization of
olefins present in the Fischer-Tropsch condensate.
The Distillate Fraction
The distillate fraction used to prepare the lubricating base oil
product of the invention represents a distillate fraction of the
Fischer-Tropsch derived product as defined above. Distillate
fractions used in carrying out the invention and the
Fischer-Tropsch derived lubricating base oil blends of the
invention may be characterized by their true boiling point (TBP)
and by their boiling range distribution. For the purposes of this
disclosure, unless stated otherwise, TBP and boiling range
distributions for a distillate fraction are measured by gas
chromatography according to ASTM D-6352 or its equivalent.
A critical property of the distillate fractions of the invention is
viscosity. The distillate fraction must have a kinematic viscosity
of about 2 or greater but less than 3 cSt at 100 degrees C., more
preferably between about 2.1 and 2.8 cSt at 100 degrees C., and
most preferably between about 2.2 and 2.7 cSt at 100 degrees C.
Another critical property of the distillate fractions and the
lubricating base oil products of the invention is volatility which
is expressed as Noack volatility, Noack volatility is defined as
the mass of oil, expressed in weight percent, which is lost when
the oil is heated at 250 degrees C. and 20 mmHg (2.67 kPa; 26.7
mbar) below atmospheric in a test crucible through which a constant
flow of air is drawn for 60 minutes (ASTM D-5800). A more
convenient method for calculating Noack volatility and one which
correlates well with ASTM D-5800 is by using a thermo gravimetric
analyzer test (TGA) by ASTM D-6375. TGA Noack volatility is used
throughout this disclosure unless otherwise stated. As already
noted above, the first distillate fraction of the invention while
having a viscosity below 3 cSt at 100 degrees C. displays a
significantly lower TGA Noack volatility than would be expected
when compared to conventional petroleum-derived distillates having
a comparable viscosity. This makes it possible to blend the low
viscosity first distillate fraction with the higher viscosity
second distillate fraction and still meet the volatility
specifications for the lube base oil and the finished
lubricant.
The Bottoms Fraction
The Fischer-Tropsch derived bottoms fraction represents a high
viscosity high boiling fraction. Typically, the bottom fraction
will have a kinematic viscosity of at least 9 cSt at 100 degrees C.
Fischer-Tropsch derived bottoms other than bright stock will
usually have a kinematic viscosity between about 9 cSt and about 20
cSt at 100 degrees C., with a kinematic viscosity of between about
10 cSt and about 16 cSt being preferred. The bottom fraction will
contain a large percent of Fischer-Tropsch wax and usually will be
solid at room temperature. In order to improve its properties prior
to being blended with the distillate fraction, it may be
advantageous to further process the bottom fraction. For example,
the bottom fraction may be hydrotreated to saturate the double
bonds and remove any impurities, such as any oxygenates, that may
be present. The bottoms fraction may also be isomerized to improve
its cold flow properties.
The Fischer-Tropsch derived bright stock may be prepared by highly
refining the waxy bottom fraction recovered directly from a
Fischer-Tropsch plant. However, since the Fischer-Tropsch syncrude
usually does not comprise a large proportion of heavy products, it
may be desirable to prepare at least part of the bright stock
through the oligomerization of the olefins present in the
Fischer-Tropsch condensate. The enrichment of the Fischer-Tropsch
condensate with olefins and the oligomerization of the olefins to
produce larger molecules has already been discussed. Typically, the
processing of Fischer-Tropsch derived materials to yield bright
stock will include dewaxing, hydrofinishing, and fractionation. As
already noted, Fischer-Tropsch bright stock is a high viscosity
material having a kinematic viscosity within the range of from
about 15 cSt to about 40 cSt at 100 degrees F.
Lubricating Base Oil Blends
Lubricating base oils are generally materials having a viscosity
greater than 3 cSt at 100 degrees C.; a pour point below 20 degrees
C., preferably below 0 degrees C.; and a VI of greater than 70,
preferably greater than 90. As explained below and illustrated in
the examples, the lubricating base oil blends prepared according to
the process of the present invention meet these criteria. In
addition, the lubricating base oils of the invention display a
unique combination of properties which could not have been
predicted from a review of the prior art relating to both
conventional and Fischer-Tropsch materials. The invention takes
advantage of the high VI of the light distillate fraction which
when blended with the heavier fraction will result in a final blend
having a viscosity which is within acceptable limits for use as a
lubricating base oil.
Lubricating base oils within the scope of the invention will
generally have a kinematic viscosity between about 3 and about 10
cSt at 100 degrees C. Generally the lubricating base oil will be
blended to a pre-selected target viscosity which is suitable for
preparing a finished lubricant intended for a particular
application. Obviously the proportions of the various distillate
and heavy fractions in the blend will need to be adjusted to meet
this desired target viscosity in the lubricating base oil blend.
The exact ratio of each of the fractions in the final blend will
depend on the exact viscosity of each fraction and the target
viscosity desired for the lubricating base oil, as well as other
desired properties such as, for example, VI, volatility, pour
point, cloud point and the like.
The lubricating base oil formed by the blending of the distillate
fraction and the heavy fraction is characterized as having a
viscosity between about 3 and about 10 cSt at 100 degrees C. and a
TGA Noack volatility of less than about 45 weight percent.
Generally, the lubricating base oil will have a viscosity between
about 4 cSt and about 8 cSt at 100 degrees C. and a Noack
volatility greater than about 12 weight percent. Commonly the Noack
volatility will be greater than about 20 weight percent. However,
if the lubricating base oil blend is intended for use in
formulating a crankcase lubricating oil, the Noack volatility
preferably will be less than about 30 weight percent. Volatility of
the Fischer-Tropsch derived lubricating base oil blends of the
invention are acceptable and are comparable to conventional
petroleum derived lubricating base oils which is surprising given
the low viscosity of the distillate fraction. The use of a
comparable petroleum derived base oil in a lubricating base oil
blend would result in an unacceptably high Noack volatility.
Generally, the viscosity index (VI) of the Fischer-Tropsch derived
lubricating base oil blend will be between about 130 and about 185.
VI is an expression of the effect of temperature on viscosity, and
it is surprising that a lubricating base oil blend prepared using a
base oil having a viscosity of less than 3 cSt at 100 degrees C.
will be characterized by such a favorable VI. As noted previously,
it is even more surprising that the blends of the invention often
realize a VI premium, i.e., the VI of the lubricating base oil
blend is higher than would be expected from an averaging of VI of
the light distillate fraction with that of the heavy fraction.
Since Fischer-Tropsch derived hydrocarbons are typically very low
in total sulfur, the total sulfur content of the lubricating base
oil usually will be less than about 5 ppm. Conventionally-derived,
solvent processed lubricating base oils will generally display much
higher sulfur levels, usually in excess of 2000 ppm.
Lubricating base oil blends within the scope of the invention will
generally have a boiling range distribution of at least 450 degrees
F. (about 232 degrees C.). Typically, the Fischer-Tropsch derived
lubricating base oil blend will have an initial boiling point
within the range of between about 550 degrees F. (288 degrees C.)
and about 625 degrees F. (330 degrees C.), an end boiling point
between about 1000 degrees F. (538 degrees C.) and about 1400
degrees F. (760 degrees C.), and wherein less than 20 weight
percent of the blend boils within the region defined by the 50
percent boiling point, plus or minus 30 degrees F. (16.7 degrees
C.). The boiling range distribution of the lubricating base oils of
the invention are significantly broader than those observed for
conventional lubricating base oils. The boiling range for
conventionally derived lubricating base oils typically will not
exceed about 250 degrees F. (about 139 degrees C.). In this
disclosure when referring to boiling range distribution, the
boiling range between the 5 percent and 95 percent boiling points
is what is referred to.
Pour point is the temperature at which a sample of the lubricating
base oil will begin to flow under carefully controlled conditions.
In this disclosure, where pour point is given, unless stated
otherwise, it has been determined by standard analytical method
ASTM D-5950. Lubricating base oils prepared according to the
present invention have excellent pour points which are comparable
or even below the pour points observed for conventionally derived
lubricating base oils. In addition, the blends containing the
distillate fraction and bright stock have been observed to display
a cloud point premium, i.e., the cloud point is significantly lower
than would have been predicted from the mere averaging of the cloud
points of the two components making up the blend. In some cases the
cloud point will actually be significantly lower than the cloud
point of either component. Preferably the cloud point of such
blends will be -15 degrees C. or less. Finally, due to the
extremely low aromatics and multi-ring naphthene levels of blends
of Fischer-Tropsch derived lubricating base oils; their oxidation
stability far exceeds that of conventional lubricating base oil
blends.
A useful property of lubricating base oils and finished lubricants
intended for use in automobile engine oils is measured by
cold-cranking simulator (CCS) apparent viscosity which correlates
with low temperature cranking. It is measured by ASTM D5293 at a
set temperature between -10 and -35 degrees C. Engine oil
specifications, e.g., SAE J300, include maximum limits for CCS
Viscosity for multi-grade engine oils. For a finished lubricant
within the scope of the invention the cold-cranking simulator (CCS)
apparent viscosity should be less than 7000 cP at -25 degrees C.
and preferably of 6500 cP or less at -25 degrees C. if the
lubricant is intended for use as a multi-grade engine oil in an
automobile engine.
Finished Lubricants
Finished lubricants generally comprise a lubricating base oil and
at least one additive. Finished lubricants are used in automobiles,
diesel engines, gas engines, axles, transmissions, and industrial
applications. As noted above, finished lubricants must meet the
specifications for their intended application as defined by the
concerned governing organization. Lubricating base oils of the
present invention have been found to be suitable for formulating
finished lubricants intended for many of these applications. For
example, lubricating base oils of the present invention may be
utilized in formulations to meet SAE J300, June 2001 specifications
for 10W-XX, and 15W-XX multi-grade crankcase lubricating oils.
Although some multi-grade crankcase oils meeting may be formulated
using only Fischer-Tropsch lubricating base oils prepared according
to the present invention, in order to meet the specifications for
some 10W-XX and most 15W-XX, it may be desirable that the
Fischer-Tropsch derived lubricating base oil be blended with a
conventional petroleum derived lubricating base oil, such as a
conventional neutral Group I or Group II base oil to meet the
specifications. Typically, when present the conventional neutral
Group I or Group II base oil will comprise from about 40 to about
90 weight percent of the lubricating base oil blend, more
preferably from about 40 to about 70 weight percent. Also
Fischer-Tropsch derived lubricating oils of the invention may be
used to formulate mono-grade engine oils, such as SAE 20 or SAE 30,
which are heavily used in many parts of the world where low
temperature performance is not critical. In addition,
Fischer-Tropsch derived lubricating base oils of the invention may
be used to formulate finished lubricants meeting the specifications
for automatic transmission fluids, NLGI Mark GC and LB greases, and
ISO Viscosity Grade 22, 32, and 46 industrial oils.
The lubricating base oil compositions of the invention may also be
used as a blending component with other oils. For example, the
Fischer-Tropsch derived lubricating base oils may be used as a
blending component with synthetic base oils, such as esters (mono-,
di-, dimer, polyol-, and aromatic), polyalphaolefins, polyphenyl
ethers, and polyglycols to improve the viscosity and viscosity
index properties of those oils. The Fischer-Tropsch derived base
oils may be combined with isomerized petroleum wax. They may also
be used as workover fluids, packer fluids, coring fluids,
completion fluids, and in other oil field and well-servicing
applications. For example, they can be used as spotting fluids to
release a drill pipe which has become stuck, or they can be used to
replace part or all of the expensive polyalphaolefin lubricating
additives in downhole applications. Additionally, Fischer-Tropsch
derived lubricating base oils may be used in drilling fluid
formulations where shale-swelling inhibition is important, such as
described in U.S. Pat. No. 4,941,981.
Additives which may be blended with the lubricating base oil to
form the finished lubricant composition include those which are
intended to improve certain properties of the finished lubricant.
Typical additives include, for example, anti-wear additives,
detergents, dispersants, antioxidants, pour point depressants, VI
improvers, friction modifiers, demulsifiers, antifoaming agents,
corrosion inhibitors; seal swell agents, and the like. Other
hydrocarbons, such as those described in U.S. Pat. Nos. 5,096,883
and 5,189,012, may be blended with the lubricating base oil
provided that the finished lubricant has the necessary pour point,
kinematic viscosity, flash point, and toxicity properties.
Typically, the total amount of additives in the finished lubricant
will fall within the range of from about 1 to about 30 weight
percent. However due to the excellent properties of the
Fischer-Tropsch derived lubricating base oils of the invention,
less additives than required with conventional petroleum derived
base oils may be required to meet the specifications for the
finished lubricant. The use of additives in formulating finished
lubricants is well documented in the literature and well within the
ability of one skilled in the art. Therefore, additional
explanation should not be necessary in this disclosure.
EXAMPLES
The following examples are included to further clarify the
invention but are not to be construed as limitations on the scope
of the invention.
Example 1
Two Fisher-Tropsch distillate fractions (designated FT-2.2 and
FT-2.4, respectively) having kinematic viscosities between 2 and 3
cSt at 100 degrees C. were recovered from a Fischer-Tropsch
syncrude prepared using a cobalt-based catalyst. Each fraction was
analyzed and their properties were compared to two commercially
available conventional petroleum derived oils (Nexbase 3020 and
Pennzoil 75HC) having viscosities within the same general range. A
comparison between the properties of the four samples is shown
below:
TABLE-US-00001 Nexbase Pennzoil FT-2.2 FT-2.4 3020 75HC Vis. @
100.degree. C. (cSt) 2.18 2.399 2.055 2.885 Viscosity Index (VI)
123 125 96 80 Pour Point, C. -37 -33 -51 -38 Noack (wt. %) 52.3
56.64 75.1 59.1
It should be noted that, although the viscosity at 100 degrees C.
of the two Fischer-Tropsch derived materials were comparable to
those of the conventional oils, the VI is surprisingly high, which
results in a much lower volatility for a given viscosity.
Example 2
A Fisher-Tropsch bottom fraction, designated FT-14, was recovered
from a Fischer-Tropsch syncrude prepared using an iron-based
catalyst. The bottom fraction was subsequently hydrotreated. The
properties of FT-14 were as follows:
TABLE-US-00002 Viscosity at 100 degrees C. (cSt) 14.62 Viscosity
Index (VI) 160 Pour Point, C. -1
Example 3
Two different Fischer-Tropsch derived lubricating base oil blends
were prepared by blending different proportions of the FT-2.4 from
example 1 and FT-14 from example 2. The proportions of FT-2.4 and
FT-14 in each blend are shown in Table 1 below:
TABLE-US-00003 TABLE 1 Wt % FT-2.2 Wt % FT-14 Lubricating Base Oil
A 60 40 Lubricating Base Oil B 35 65
The properties for each of the lubricating base oil blends are
summarized in Table 2 below:
TABLE-US-00004 TABLE 2 Lubricating Lubricating Base Oil A Base Oil
B D-2887 Simulated TBP (WT %), .degree. F. TBP @0.5 593 596
(Initial Boiling Point) TBP @5 616 634 TBP @10 630 659 TBP @20 656
708 TBP @30 680 765 TBP @40 705 1015 TBP @50 730 1032 TBP @60 760
1049 TBP @70 996 1065 TBP @80 1027 1089 TBP @90 1057 1136 TBP @95
1079 1182 TBP @99.5 1132 1251 Boiling Range 463 548 Distribution (5
95) Viscosity at 40.degree. C. 21.00 38.62 Viscosity at 100.degree.
C. 4.969 7.718 Viscosity Index 174 174 Pour Point, .degree. C. -29
-19 CCS at -25.degree. C., cP* 2293 CCS at -35.degree. C., cP 1058
8570 TGA Noack 37.85 22.47 *This property represents cold-cranking
simulator (CCS) apparent viscosity which is a measure of low
temperature cold-cranking in automobile engines determined by ASTM
D-5293.
It should be noted that both Fischer-Tropsch blends had
volatilities, as measured by TGA Noack, which was suitable for
blending engine oils. It should also be noted that the VI of each
of the blends was higher than the VI of either FT-2.4 or FT-14
indicating that the blends were realizing a VI premium.
Example 4
The properties of the Fischer-Tropsch derived lubricating base oils
as shown in Table 2 above may be compared to the properties of
commercially available petroleum derived conventional Group I and
Group II light neutral base oils as summarized in Table 3
below.
TABLE-US-00005 TABLE 3 Chevron Generic Gulf Exxon Texaco Gulf Coast
Coast Americas 100R Solvent 100 H.P. 100 Core 100 API Base Oil II I
II I Category (API 1509 E.1.3) D-6352 Simulated TBP (WT %),
.degree. F. TBP @5 659 647 TBP @10 677 672 TBP @20 703 703 TBP @30
723 725 TBP @50 756 761 TBP @70 786 796 TBP @90 825 839 TBP @95 842
858 TBP @99.5 878 907 Boiling Range 219 211 Distribution (5 95)
Viscosity at 40.degree. C. 20.0 20.4 20.7 20.2 Viscosity at
100.degree. C. 4.1 4.1 4.1 4.04 Viscosity Index 102 97 97 95 Pour
Point, .degree. C. -14 -18 -15 -19 CCS at -25.degree. C., cP 1450
1430 1550 1513 CCS at -35.degree. C., cP >3000 >3000 >3000
>3000 Noack Volatility, wt % 26 29 25.5 29.3
A comparison of Table 2 and 3 illustrate that the Fischer-Tropsch
derived lubricating base oils have a similar Noack volatility to
conventional Group I and Group II light neutral oils. The kinematic
viscosity of Lubricating Base Oil A was comparable to that of the
Group I and Group II light neutral oils while that of Lubricating
Base Oil B was significantly higher. Lubricating Base Oil A
displays a lower pour point than the conventional light neutral
oils. The Fischer-Tropsch derived lubricating base oils of the
invention also display significantly better VI values.
Example 5
A lubricating base oil blend was prepared which contained 25 weight
percent of FT-2.2 and 75 weight percent of FT-14. The kinematic
viscosity at 100 degrees C. was found to be 9.007 and the VI was
173. Once again the blend displays a VI premium over the VI's of
both FT-2.2 and FT-14.
Example 6
A Fisher-Tropsch distillate fraction designated FT-2.5 was blended
with a Fischer-Tropsch derived bright stock designated FT-BS that
was prepared by oligomerizing the olefins in a Fischer-Tropsch
derived feed. The properties of the two Fischer-Tropsch derived
feeds were as follows:
TABLE-US-00006 FT-2.5 FT-BS Vis. @ 100.degree. C. (cSt) 2.583 30.12
Viscosity Index (VI) 133 132 Pour Point, C. -30 -46 Cloud Point, C.
-16 -10 Noack (wt. %) 48.94
Two different Fischer-Tropsch derived lubricating base oil blends
were prepared and the respective proportions of FT-2.5 and FT-BS in
each blend are shown in Table 4 below:
TABLE-US-00007 TABLE 4 Wt % FT-2.5 Wt % FT-BS Lubricating Base Oil
C 70 30 Lubricating Base Oil D 30 70
The properties for each of the lubricating base oil blends are
summarized in Table 5 below:
TABLE-US-00008 TABLE 5 Lubricating Lubricating Base Oil C Base Oil
D D-2887 Simulated TBP (WT %), .degree. F. TBP @0.5 (Initial
Boiling Point) 599 604 TBP @5 617 634 TBP @10 630 664 TBP @20 656
728 TBP @30 684 809 TBP @40 711 1048 TBP @50 739 1114 TBP @60 773
1165 TBP @70 809 1210 TBP @80 1111 1261 TBP @90 1226 1312 TBP @95
1288 1335 TBP @99.5 1349 1373 Boiling Range 671 701 Distribution (5
95) Viscosity at 40.degree. C. 20.70 84.14 Viscosity at 100.degree.
C. 4.799 12.58 Viscosity Index 162 147 Pour Point, .degree. C. -23
-33 Cloud Point, .degree. C. -16 -23 CCS at -20.degree. C., cP*
4,017 CCS at -25.degree. C., cP* 6,665 CCS at -30.degree. C., cP
1,186 11,911 TGA Noack 34.55 14.52 *This property represents
cold-cranking simulator (CCS) apparent viscosity which is a measure
of low temperature cold-cranking in automobile engines determined
by ASTM D-5293.
It should be noted that both Fischer-Tropsch blends had excellent
VI, low pour points, and low cloud points. Note particularly the VI
of the blends which demonstrate a VI premium when compared to the
VI's for FT-2.5 and FT-BS. Also note the significant improvement in
cloud point as compared with FT-BS. Note that the cloud point for
lubricating base oil D displays a cloud point premium, i.e., the
cloud point is significantly lower than that for either FT-2.5 or
FT-BS. Base oils with a premium cloud point have utility in
products which require cold filtration, such as, for example,
refrigeration oils. Base oil C, although too high in volatility to
be used in engine oils alone, can be further blended as a minority
component for engine oils, or used as a majority component in many
other lubricant applications, such as, for example, transmission
fluids, industrial oils, diluent oils, spray oils, process oils,
hydraulic oils, and the like. Base oil D can be used to make 15W 40
engine oil with no added viscosity modifier.
* * * * *